1. Field of the Invention
This invention relates to the manufacture of parts, such as, for example, aircraft, boat and automobile panels, embodying resins and/or adhesive materials.
2. Description of the Prior Art
The curing of shaped composite parts comprising fibers such as graphite or Kevlar fibers impregnated with thermosetting resins or the bonding of thin metallic or metallic and resinous laminates with thermosetting adhesives is recognized as an effective method of manufacturing lightweight, high strength panels, etc.
In carrying out such procedures with composites, the involved part is placed on a shaped tool or mold in an uncured and somewhat pliant state. A relatively high degree of temperature and pressure is then applied thereto to remove air, moisture and volatiles from the material during the forming and curing operation.
In bonding thin laminates of metal or metal and a composite material together, a thermosetting adhesive is sandwiched between them and they are likewise placed on a shaped tool and subjected to a high degree of temperature and pressure to remove the air, volatiles, etc. therefrom during the forming and bonding operation.
The bonding of shaped parts is generally accomplished by placing the materials to be bonded on a shaped tool and covering them with a flexible porous breather pad after which a vacuum bag is placed thereover and secured to the tool. This assembly is then heated in an autoclave while vacuum is pulled on it to withdraw air and volatiles from the bag and resinous material and from any adhesive present during the curing phase and to impress the part being formed against the tool. The breather pad enables vacuum to be pulled uniformly on all areas of the part and/or the adhesive. The autoclave is pressurized during this procedure to help force the part to intimately fit the contour of the tool and to aid in removing the air, volatiles, etc. therefrom.
Heretofore, breather pads have been formed of intertwined fibers of polyester material and have been generally satisfactory when the curing temperatures were held to little more than about 300.degree. F. However, as composite materials and adhesives of improved strength and other desirable qualities were developed they were found to require higher curing temperatures than this, as well as higher than the conventional forming pressures then employed. This caused the polyester fibers of the breather pad to soften and compact or even fuse together thus closing the interstices between the intertwined fibers and preventing uniform evacuation of volatiles, etc., from all areas of the material being treated as well as any adhesive present. Accordingly, the resulting part instead of being formed into a solid dense structure would tend to contain zones of weakened structural integrity.